Thermostability and decomposition of the (Bi,Pb)2Sr2Ca2Cu3O10 phase in silver-clad tapes

Abstract

The stability of the Bi2−xPbxSr2Ca2Cu3O10 (Pb-2223) phase contained in silver-sheathed oxide-powder-in-tube specimens has been investigated by x-ray diffraction, transmission electron microscopy, and energy dispersive x-ray analysis. Silver tubes loaded with Pb-2223 precursor powders were processed into tapes using established metallurgical techniques. The tapes were heat-treated in a specially designed equilibration apparatus at selected temperatures (800–845 °C) for a range of times (10–5500 min) and quenched in liquid gallium held at ∼40 °C. The results showed that the Pb-2223 phase is stable in a limited temperature interval between 810 and 830 °C in 7.5% oxygen. At 800 °C, this phase decomposes to Bi2Sr2CaCu2O8 (2212), Ca2PbO4, and CuO; while at temperatures ≥840 °C it partially melts with precipitation of Bi2Sr2CuO6 (2201) and Ca2CuO3. The effects of the silver cladding on the Pb-2223 phase stability and microstructure are also discussed.